DESIGNING POWER SUPPLIES FOR TUBE AMPLIFIERS MERLIN BLENCOWE PDF

I have to admit that I had low expectations, not because I was prejudiced against its author, but for the simple reason that most books intended for DIY audio electronics—and perhaps particularly for those intended for tube-audio—tend to be too simple-minded. It is almost as if the publisher and writer assume that making the big jump from the remote control to the soldering iron is in itself a feat of such towering skill, endurance, strength, and imagination that would be asking too much to expect the poor audiophile to learn and understand complex concepts as well. Thus, they give us too little—for our own good, as they see it. Blencowe's book, on the other hand, is not a piece of fluff, as he does not insult our intelligence nor withhold the goods.

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I have to admit that I had low expectations, not because I was prejudiced against its author, but for the simple reason that most books intended for DIY audio electronics—and perhaps particularly for those intended for tube-audio—tend to be too simple-minded. It is almost as if the publisher and writer assume that making the big jump from the remote control to the soldering iron is in itself a feat of such towering skill, endurance, strength, and imagination that would be asking too much to expect the poor audiophile to learn and understand complex concepts as well.

Thus, they give us too little—for our own good, as they see it. Blencowe's book, on the other hand, is not a piece of fluff, as he does not insult our intelligence nor withhold the goods. Yet, Designing Power Supplies for Tube Amplifiers is not a tedious academic book, stuffed with footnotes and turgid prose, a textbook that one is forced to buy and which we read only under duress and which we are happy to be rid of once our class has ended.

Blencowe knows who his DIY readers are and what their hopes and expectations are. He knows that most solder-slinging audiophiles stumble when it comes to designing and building a power supply for their project. He also knows that the audio circuitry makes different demands on a power supply and that tube audio makes extra demands, because of higher voltages involved.

He knows that finding such information is difficult, as the average power-supply book is intended for a different audience. Thus, his book wisely ignores switching power supplies, but generously covers tube rectification, series and shunt regulation, and heater power supplies. Nor is his book merely a historical summery, as many many tube-amplifier books tend to be, covering only old designs that your grandfather would recognize.

Instead, Designing Power Supplies for Tube Amplifiers summarizes existing tube-audio power supplies, but also reveals new techniques and designs. Be warned, you will encounter many formulas in Designing Power Supplies for Tube Amplifiers, but do not worry, as only simple algebra is required.

In addition, all the many schematics are cleanly laid out and easy to understand. So far, I haven't found a single schematic typo, which is a laudatory achievement indeed. And the book's layout is good, comprising ten chapters, the first chapter covering power transformers and the last, voltage control input AC voltage control. One oddity is finding what should have been the eleventh chapter Cooling and Heatsinking nested in chapter seven, "Series Voltage Stabilizers.

In fact, it was only in reading his explanation of calculating heatsink requirements that my eyebrows began to knit, my forehead furrowed. For example, although he praises silicon thermal pads, so much tidier, he says nothing about the up to 1. Instead, I was surprised to see him give 0.

The Elliott Sound Practices web site offers wonderful heatsinking explication, guidelines, and design practices. In spite of the word "tube" in the book's title, I instantly assumed that Mr. Blencowe was a Brit, not just because his first name is Merlin. Under the dust jacket, the book's spine and its inner title page reveal the book's true title, Designing Power Supplies for Valve Amplifiers.

Moreover, Mr. Blencowe writes like a Brit, abundantly displaying good manners, never lapsing into excessive informality deferential, glad to be of use, politic, cautious, and meticulous Do not get me wrong here, as I greatly prefer such a style over the "Hey Dude, pass me the roach, I mean alligator clip" style of many guitar amplifier books.

Still, for this American, Mr. Blencowe's over reliance on a somewhat passive and circumlocutory exposition wearies. For example, he begins a section titled "Relative output voltages of rectifier circuits" thus:. There are two or three power-supply topologies which are seen again and again in valve amps, and are regarded as almost standard, being more-or-less copied from the popular, early amps.

However, it is worth noting that these designs are not compulsory; there are many ways to arrange the same transformer and rectifier, depending on the output voltage we need. After the first hundred pages, I felt like slapping him on the back and telling him, "Just spit it out man" and I am a rabid anglophile.

As I read the above paragraph, my mind translated it into American thus:. Most modern valve amplifiers hold a power supply identical to those found in old valve amplifiers, which seems to imply that these old topologies are standards not to be altered—yet these hoary topologies are neither compulsory nor necessarily best. Depending on our design goals, the same transformer and rectifiers allow many different arrangements, indeed, often better arrangements.

Perhaps, I am making a Maugham out of a molehill, you know, Somerset Maugham as few readers are likely to read this book in a single sitting as I did and his prose is still far more spritely and readable than any modern electronics textbook I have read—and I have read plenty. In general, electronics textbooks written before are lucidly and gracefully composed.

The urge to make some snide comment on the modern educational system was almost impossible to resist, such as: How could so much have been achieved without a Department of Education, establish in ? Fortunately, I held firm In conclusion, in spite of a few minor, very minor criticisms, I highly recommend this book, for beginners and masters alike. Beginners should read the first five chapters over and over again, as they cover essential material, such as transformer selection, rectification, and filtering; particularly, the chapter on LC smoothing filters, as most tube fans know nothing about the problem of LC resonance.

Advanced practitioners will find much to like in these and in the following five chapters. Many pure tube-based and solid-state-based and hybrid solutions are illustrated; there is even a quite Janus-like shunt regulator that utilizes both feedforward and feedback to produce clean, steady DC voltage, page ; And the last chapter is a must read, as it covers the problem of too little or too much wall voltage and some possible solutions.

Today, however, it is not enough that a book be well written, illustrated, researched, and organized, as it must pass the new test, the web test: If I can find all the same material on the web for free, do I really need to buy this book? In the case of, Designing Power Supplies for Valve Amplifiers, the answer is yes, you need the book, as you cannot find it all on the web; no doubt, many portions can be found, but not everything—and certainly not in such a well packaged format.

Additionally, you can put your trust in Mr. Blencowe's efforts. Can you say that about all that you find in a Google search? Starting with the compulsory throat clearing, let's look at two old designs. The first uses the famous LM positive, adjustable voltage regulator and a high-voltage triode. I remember seeing this schematic in an old National Semiconductor data sheet over 30 years ago. The low-voltage regulator establishes and maintains the fixed output voltage, while the high-voltage triode shields the solid-state device from lethal voltages.

The LM strives to maintain a constant 1. As tubes grew ever less popular in sober electronics, this circuit was expunged from later data sheets. The single triode had been replaced by two high-voltage transistors and some extra support circuitry. Well, all of this is old hat.

What intrigued me was this question, Is it possible to make a high voltage regulator based on an LM? No, not a high-voltage negative regulator, which would be merely a mirror image of the above circuit, with PNP transistors replacing NPN types, my goal was a positive high-voltage regulator.

No one asked me this question; I was just giving myself a brain teaser. My first thoughts were that it would certainly be possible to create a shunt regulator, such as the following. Where to start? This high-voltage shunt regulator looks far more complex than it really is.

The LM is in control, measuring the output voltage and applying corrections as needed. In other words, they are not safety devices the way the unmarked diode is 1N in the schematic. The zener both establishes a fixed reference voltage and a current path in parallel with the LM The LM will use all its considerable negative feedback to keep a steady 1. In other words, the LM is constantly evaluating the voltage it sees at its output and adjustment pins, as it strives to maintain a fixed voltage difference between the two.

The LM really doesn't know that it is the heart of an elaborate high-voltage positive regulator; all it knows is what is happening at its output and adjustment pins.

Ground isn't a signal source. Actually, in a voltage regulator, it is THE signal source, as a voltage regulator can be viewed as being a powerful unity-gain amplifier, with a huge fixed DC offset and whose signal source is ground.

Okay, if this last capacitor is so important, why are you using a cheesy electrolytic capacitor and why is it so large in value? But the capacitor also terminates into the ohm resistor, which is effectively grounded at its other end. Of course, this would also greatly reduce the current flow through both the zener and the LM negative voltage regulator.

Not good. But if we place a power resistor s in parallel with the resistor string, the LM and zener can still get the current they require. National Semiconductor makes or used to make a high-voltage version of the LM, which can withstand 47V between its input and output pins.

In addition, our shunting triode might require even greater potential cathode swings. This is the baby-step circuit before we move on the actual circuit; nonetheless, it might prove adequate for many preamp and line-stage amplifier applications.

Although the negative bias voltage tap is usually only found on big power transformers that were intended for use in tube power amplifiers. Now we arrive. It can. The following schematic is stripped down, so as to leave its operation on display without the clutter of the safety and performance-enhancing components.

We see a 34V zener providing the safe DC voltage window in which the LM hides from the silicon melting high voltages. We also see the pass device, the triode, being controlled by the LM As LM increases in conduction, the triode sees its grid voltage increase; as LM decreases, the grid voltage falls. Note that a 1. At idle, with no external load, the triode and the In the schematic, the LM conducts 3mA, while the zener conducts 17mA. With an external load attached, the triode might undergo a current flow of mA, while the As it stands, this high-voltage series regulator is interesting, but it is a bit naked and it offers limited grid-voltage swings.

The following deluxe version addresses both of these concerns. Yes, it looks complicated, but the operation is the same.

By the way, the LM only sees a 9. Thus, its maximum power dissipation is only 0. Likewise, the MJE never dissipates much heat, so it also can be run naked. I would use either a 10W resistor or two 5W 24k resistor in parallel.

My guess is that the circuits are still too naked, requiring more protection devices, such a resistor in series with the LM's adjustment pin and some of the capacitors. Speaking of guts, here is what those three pins connect to internally.

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View Larger Image. Has little wear to the cover and pages. Contains some markings such as highlighting and writing. Supplemental materials are not guaranteed with any used book purchases.

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Designing Power Supplies for Valve Amplifiers

Designing Power Supplies for Tube Amplifiers. Hardback, pages. Attention: I'm sorry to say this book has been removed from print. I will probably write a second edition eventually, but it could take years. This book is therefore unavailable until further notice.

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